Oilfield fluids (e.g., oil, gas, and water) are generally complex mixtures of aliphatic hydrocarbons, aromatics, hetero-atomic molecules, anionic and cationic salts, acids, sands, silts, clays and a vast array of other components. The nature of these fluids, combined with the severe conditions of heat, pressure, and turbulence to which they are often subjected, are contributory factors to the formation and deposition of unwanted contaminants, such as scales, salts, paraffins, corrosion, bacteria and asphaltenes in oil and/or gas production wells.
A common site for the formation and deposition of such contaminants is the annular space between the production tubing and casing of oil or gas wells. The annulus may be a static area or may produce gas or liquid. In low pressure gas wells, such as coal bed methane wells, the gas is produced up the annulus and the liquid (water) is allowed to fall to the liquid level and removed via a submersible pump up the tubing. Such undesirable substances as salt, scales, paraffins and asphaltenes, form due to the pressure changes at the perforations. Alternatively, such substances form due to comingling of incompatible waters from one set of perforations to another.
The formation and deposition of such unwanted contaminants decrease permeability of the subterranean formation and reduce well productivity. For instance, in some completions, the presence of scale in the annulus may make it difficult or impossible to remove the tubing for servicing. While there are a number of approaches to these production problems in the patent and journal literature, nearly all of them deal with the problem on an individual basis as they form, which can be costly when numerous problems arise during production. A further problem with such an approach is the cost of tracking and monitoring such production problems. For example, the technique of “downhole squeezing” is commonly used to address oil field scale formation, wherein a slug of the well treatment composition is injected into the annulus, using a pre-flush, squeeze, and overflush treatment before the well can be returned to normal function. However, the overflush process often flushes a significant portion of the well treatment agent such that the remaining well treatment agent is gradually removed from the surface as oil production continues. Thus, further descaling treatments are typically required. Further, such treatment methods are typically inefficient in that contact with all of the surfaces of the tubing external and casing internal is not completely achieved. As a result, large quantities of the well treatment agent are required.
Alternative treatment methods have therefore been sought for introducing well treatment agents into oil and/or gas wells and especially between the annular surface between the tubing and casing.